Variable section nozzle neck



Il'l "KIS M. MENARD VARIABLE SECTION NOZZLE NECK 4 Sheets-Sheet 1 Irr1.1;)I/l//1 zlllllllllllbl//l//lll lll/11111111;

April 22, 1958 Filed May 6, 1956 4 Sheets-Sheet 2 M. MENARD VARIABLESECTION NOZZLE NECK April 22, 1958 Filed May e, 195e April 22, 1958Filed May 6, 1956 M. MENARD VARIABLE SECTION NOZZLE NECK- 4 Sheets-Sheet3 lml l1 I IH" .1.)

April 22, 1958 M. MENARD 2,831,505

VARIABLE SECTION NOZZLE NECK Filed May e, 195s 4 sheets-sheet 4 A B c \Bs s, s s, a* 6 (il), NL

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United States Patent() VARIABLE SECTION NOZZLE NECK Maurice Menard,Saint-Cyr, l'ance, assignor of one-half i? Conservatoire National desArts et Metiers, Paris,

rance Application March 6, 1956, Serial No. 569,792

Claims priority, application France June 29, 1951 6 Claims. (Cl. 13S-45)This invention relates to a wind tunnel for testing devices such asmodels at high air speeds.l The invention particularly relates to a windtunnel in which the crosssectional area of the inlet end of the tunnelmay readily be changed, whereby the speed of the air in the passage maybe varied. The wind tunnel of the invention is particularly adapted forproducing streams of air travelling in the range from subsonic to asubstantial number of times the speed of sound.

This application is a continuation-in-part of application Serial No.272,162, led February 18, 1952, now abandoned.

Prior variable air-speed wind tunnels of the type Wherein the electivearea of the tunnel passage may be changed have been relativelyunsatisfactory both as to construction and operation. Some prior tunnelsof this type employ replaceable xed entrance ends or nozzles. To changethe effective cross-sectional area of the entrance end of the tunnelthepnozzle must be changed, an operation which usually requires severalhours. This not only adds considerably to the labor cost of the testingoperation, but also, in elect, wastes valuable time in which the testequipment is idle. Further, this type of wind tunnel precludes changingthe effective cross-sectional area of the tunnel while it is inoperation, but also does not allow a smooth change in such area, sincethe different replacement nozzles must of necessity differ appreciablyfrom each other.

Other prior valuable air-speed Wind tunnels have employed exibledeformable walls forming the throat of the tunnel, the walls beingdeformed as by jacks working from the outside of the tunnel. Such exiblethroats are very expensive to make. Further, thecontour of the throat isdiiiicult to control and reproduce, and in many instances, in certainadjusted deformed positions, the contour of the throat is far fromideal.

The wind tunnel of the present invention is of simple, ruggedconstruction, easily made and operated. The lconstruction of the tunnelis such that a marked change in the eiective cross-sectional area of theentering end of the tunnel may be made, even under operating conditions,by one person in a very short time. The change in crosssectional area ofthe entering end of the tunnel of the invention is continuous, and thusmay be varied in in- 'nitely small steps. This the behavior of a devicesuch as a model may readily be investigated fully in all portions ,of arange of air speeds from subsonic to well above the speed of sound.

The wind tunnel of the invention is shown in a preferred embodiment inthe accompanying drawings forming part of the specification. "4 In thedrawings j Fig. l is a fragmentary view in longitudinal axial sectionthrough the entrance or throat end of the tunnel, the zone oftheadjustable ow-controlling members or bosses, and aportion of the testingsection of the tunnel, the sectioning plane lying normal to the first,parallel walls of the tunnel.

'42,831,505 Patented APH 2.22-19@ Fig.2 is a view similar to Fig. l butwith the sectioning plane displaced 90 about the longitudinal axis ofthe tunnel from the sectioning plane of Fig. l, the section of Fig..2being taken along line 2-2 of Fig. 1.

Fig. 3 is an end elevation of the wind tunnel from the throat orentering end thereof, the view being taken from line 3-3 of Fig. 1.

Fig. 4 is a plan of an air-ow-controlling boss of the wind tunnel of theinvention.

Fig.5 is a side elevation of such boss.

Fig. 6 is an end elevation lof the boss of Figs. 4 and 5, the View beingtaken from line 6 6 of Fig. 5.

Fig. 7 is an enlarged view in section of a portion of the wind tunnelwall at the location of an air-ilow-controlling boss, and of parts ofthe mechanism for adjusting the boss longitudinally of the tunnel,certain of the parts being shown in elevation, the section being takengenerally along the line 7+7 of Fig. 2. 4 Fig. 8 is an enlarged view insection of parts of the mechanism for adjusting the fboss, the mechanismbeing broken away in portions ,thereof to save space in illustration,the section being taken generally along the line 8 8 of Fig. 2, certainof the parts being shown in elevation.-

Fig. 9 is a schematic view of the portion -of the wind tunnel at theair-ow controlling bosses, and related graphs showing Variation in therate of flow of air in the tunnel at various zones of the bosses. v

Fig. 10 is a graph plotting AM, the magnitude of the oscillation M ofthe Mach number` on the axisof the throaty of the tunnel, against therate of change .of the pressureV of the air with respect to distancemeasured alongthe axis of the tunnel.

Referring nowto Figs. l, 2, and 3, it will be .seen that the illustratedpreferred embodiment `of the wind tunnel, generally designated 10, is ofrectangular cross-section, and has a first pair of opposite parallelplane walls 14, shown vertical in Fig. 3, and a second pair of oppositewalls 11 and 12, shown as the-bottom and top walls, respectively, inFig. 3. Walls 11, 12, and 14 define a longitudinally extending passage13 through the tunnel. The walls 11 and 12 are mirror images of eachother. From generally the line 11S-18 rearwardly (toward the right inFigs-1 and 2) the walls 11 and 12 are shown as being plane and parallel.If desired, such portions of walls 11 and 12 may diverge slightly in arearward direction. In any event, in such portion walls 11 and 12 may besaid to be at least generally parallel.,y The forward portion 16 ofwalls 11 and 12, to the left of line 18--18 in Figs. 1 and 2,constitutes a flared throat; portions 16 of walls 11 and 12 mergesmoothly with the rearward plane portions thereof.

The wind tunnel of the invention is provided with means whereby theeffective cross-sectional area of the-throat may be adjusted, whereebythe speed of travel of the air stream through the tunnel passage may beselectively varied. The tunnel. shown is provided with two similarbosses 17, oppositely disposed on sidewalls 14 so as to deiine aconstricted zone |between them. The bosses 17 are adjustablelongitudinally of the tunnel between the position indicated in thedotted outlines 17 in Figs. 1 and -2,

in which they lie largely forwardly of the line 18--18,` to

eiective cross-sectional area of the throat ofthe tunnel, rforwardadjustment of the bosses decreasing such area,

and thus the rate of flow of air through the throat and thus i thetunnel,land4 rearward adjustmentof the bosses increas- '1 ing such areaand rate of air ow. Bosses 17, in all their adjusted positions, arellocated forwardly of the testing section 23 of the tunnel.

The bosses 17 are rigid similar bodies which are mirror images of eachotherand, as shown, .are similarly positioned on .the walls 14 .of thetunnel symmetrically'as regards the longitudinal center lines of theirrespective walls 14. The configuration of the'bosses will be ymoreapparent from a consideration of Figs. 4, 4S, and 6. Each boss issomewhat narrower 'than the distance between opposite walls '11 and 12.Each bosshas a dat outer face, shown in Fig. 5 as lying on the'planeABC. The boss is symmetricalV with respect to the longitudinal planethrough pointsAC and lying normal to the plane ADCE Fig. 4. The'innersurfaceof the boss is convex, the curve AB (Fig. 5) preferablybeingaquar-terof an ellipse with a half minor axisBB and a half major axisAB. `The curve DBF. (Fig.6)'is shownas a half circle, although'it may be`made as ,half anel1ipse, if desired. The curve'BC (Fig. 5) is a.smoothlong reverse curve, theboss tapering to a pointed feather edge atC. "The effect of such curvatures of Avarious portions -of the innerface of the boss is to makesuch face smoothly streamline. `In apreferred construction, the ratio and the ratio BB/DE is `afunctionofthe maximum Mach number at which Vthe tunnel is to operate. The bosses17 are mounted with their plane `outer faces againstthe inner surfaceofthe respective Wall'14 of the tunnel. The bosses rare adjusted bybeing slid along walls y14'between the solid line positionto that shownat 17'. Preferablythe bosses are interconnected so asto be adjustedsimultaneously by operation of one adjusting means, which is shown morelclearly in Figs. 7 and`8.

As shown in these figures, mounted centrally of each wal114of the tunnelis a longitudinally rectangular rodlike 'member 21 which'slides alongthe inner surface of the Wall. The forward, leading edge of boss 17 ispreferably connected to the innertrailing edge of member`21 as by beinglwelded thereto. Connected to the rear .end of member 21 land alignedtherewith is a thinner rectangular rod-like member 24 which also slidesalong the inner face of wall.1'4. The two ends of member 24 are attachedto boss 17 at a recess in the outer fiat face of the boss. Inwardly ofmember 24 boss 17 is longitudinally slotted .at .22'to provide space fora hold-down yoke A29, which retains members 21, 24, and boss 17vforcibly in contact withthe inner face of wall 14. `Yoke 29 forms thehead of an elongated stem 26 of ahold-down member 25 which projectsthrough longitudinal slot 27 in wall 14. Member 25 includes a coilcompression spring 30.acting, in effect, between wall 14 and the outerend of the stem of member 25. Each holddown member .is enclosed in aprotective container 31. Positioned forwardly ofthe mouth 'of the tunnelon each side thereof, and supported on central extensions 41 of wallsV14 thereof, are further protective enclosures 36 containingmechanismfor llongitudinally adjusting each member 21 and .with it therespectivebioss 17. In each enclosure there is a pinion 34, keyed toshaft 35, the pinion meshing witha rack gear 32 on the outer face ofmember 21. Enclosure 36 also contains the main part of a hold-downbracket 37, the inner end of which is formed as a yoke projectingthrough a slot in wall 14 and overlies member 21 to hold it strongly inengagement with the Ywall 14. A coil compression spring 40 acts `betweenwall 14 and the outer end of the holddown member.

Asshown in Fig. 8, shafts .35 maybe drivingly connected so that the twobosses 17 may be adjusted simultaneously in vthe same direction and tothe same extent by a single adjusting means. Connected to supports 41are transversely extending (vertical in Figs. 2 and) lparallel members42 which serve to support closures 43 and members journalling the upperends of shafts 35. Betweenclosures 43 there extends a transverse shaft'46 which carries on its outer ends bevel gears 45 meshing with bevelgears 44 on the upper ends of shafts 35, as shown in Fig. 8. Mounted onshaft 46 is a worm gear 47 which meshes with a worm (not shown) on shaft49 joui-nailed in a fixed support (not illustrated). Turning of shaft 49by hand knob'50 will thus cause lequal travel of bosses 17 in the samedirection longitudinally ofthe tunnel. A .disconnectable coupling, asshown, may be interposed in shaft 46 between worm gear 47 rand'theleft-hand pinion 45 to allow initial. identical positioning of the twobosses 17.

As hasbeen pointed out above, the wind tunnel of the invention iscapable of use to produce a high speed air stream which is adjustable asto speed'in a range from subsonic to at least several times the sonicspeed. Adjustment of the speed of air travel through the testing sectionof the tunnel at subsonic Aspeeds iselected tty-,suitable adjustment ofthe exhaust .blower for theftunnel. When the tunnel `isoperated with4the air stream travelling through .the `testing section thereofat-thespeed of sound or above, the speed of air travel through such section isdetermined by the ratio S/Sc (see Fig. 9),wh'crcin S is thecross-section of the testingsection, andScAis the cross-section of thenarrowest Azone ofthe tunnel. .Under-such conditions the speed of flow`of the air increases as the jsectionincreases (in `the .zoueSc-C), andbecomes constant in the testing section 23. p l

In operating the wind .tunnel `of .the invention, the bosses 17 are.first moved .to .thefurthest upstream position (17') in the convergentmouthofthe tunnel. `,Upon starting the blower, vthe tunnel then operateslike a customary subsonic wind tunnel. Whenthe blower `has acceleratedsufficiently for the air to reach the Aspeed of soundin thetestingsection, the bosses are :progressively moved downstream fromposition 17 toward :position 17-(Figs. land 2), thus progressivelydecreasing the area of air -liow and increasing the Mach number in thetesting section. Themaximum. Mach number is obtained when the bosses areVin the fulllineposition there shown. Adjustment of the bosses betweenpositions v17' and 17 isA continuous, andmaybe made with the tunnel in.operation. Such adjustment is easily efected,.a typical'tunnel made inaccordance with the invention being customarily adjusted to vary.the;Mach knumber between 0.'6.and'l1;8 in three minutes. `With such`embodiment of the ltunnel theMach number can be continuously yadjustedupto 3, although this is not the highestMachnumber obtainable by useofthe invention. I

VIn wind tunnels a substantial uniformity of speedoflair flow inthetesting section is necessary for accuracyoftes't results. The morenearly uniform the air speed, lthe more accurate the results. Ithas beenfound that vthe wind tunnel of the invention, employingbosses u17-'ofthe`disclosed conguration, shows a variationof 'Mach number in the testingsection of AM/m=i0.002.

In `the schematic view of (Fig. 9 the minimum crosssection of the throatof the wind tunnel is 'designatedSm and the cross-section of the testingsection of `tlxotunel vils-designated S. An isentropic expansion occurs'fromJSc to S. By applying Bernoullis and the continuity" .equation forliow of elastic Huid, the required value of Mach number M determinesSISC. Since thebosses `17 'are of predetermined shape, the ratio S/Scgives ,the ratio -BB/DE, where BB' and DE are two of `the,aboveiliscussed dimensions of each boss 17. v

The aerodynamic quality required ofthe-wind 'tunnel determines the valueof the ratio BBYB'C (Figs. 4,15, and 6) through the use -of anexperimental curve,"shown in Fig. l0, which was determined by numeroustests.

In Fig. 9 the ,bosses areshown cut'by-.sever'altransverseplanes numbered0, -1,2, A3, 4. Inthezon'e Yof plane l the area of air liow AS1determines the ratio S1759. This ratio in turn determines the speed oftravel of air at plane 1 according to Bernoullis and the continuityequations. The air pressure at each of planes 1, 2, 3, 4, can thereforebe determined.

The curve l (upper curve of Fig. 9) indicates the pressure of the air inthe tunnel as a function of the posi* tions 1, 2, 3, 4. At the points 1,2, 3, 4 the slope of the curve l is measured as follows:

Slope of curve I at 1 (Q des Slope of curve I at 2 (di dx3 Slope ofcurve I at 3 (at dell Slope of curve I at 4 A theoretical curve Il(lower curve of Fig. 9) indicates the evolution of dp/dx as a functionof the abscissa. At the point 0 the curve II shows a slope of anddescribed a preferred embodiment of a variable speed wind tunnel inaccordance with the invention, it

will be understood that such embodiment is illustrative` only, since theinvention is capable of considerable variation as to details. Theinvention is, therefore, to be defined by the scope of the claimsappended hereto.

What I claim and desired to secure by Letters Patent is: 1. A windtunnel comprising a rectangular sectioned duct having a passagetherethrough and having an inlet and an outlet end and a testing sectionbetween such ends, said duct having two first opposite plane andparallel walls, the other two second opposite walls being initiallyconvergent at the inlet end and then at least generally parallel, atleast one rigid boss located in the duct adjacent the inlet end thereofsaid boss having a plane outer face engaging a rst inner wall of theduct and a streamlined inner face forming a portion of the wall of thepassage, and means for displacing the boss longitudinally of the ducttoward and away from the inlet end thereof from a furthest outwardlyadjusted position in which at least the forward end of the boss lieswithin the inlet end of the duct to a furthest inwardly adjustedposition in which the boss lies retracted into the duct beyond theconvergent portions of the second walls of the wind tunnel, so as tovary the cross-sectional area of the inlet end of the wind tunnel.

2. A wind tunnel as claimed in claim l, in which the boss is narrowerthan the width of the irst walls and lies substantially centrally of onefirst wall.

3. A wind tunnel as claimed in claim 2, in which the boss is symmetricalabout its longitudinal mid-plane nor-Y mal to the lirst walls of thetunnel, and the inner face of the boss is smoothly convex;

4. A wind tunnel comprising a rectangular sectioned duct having apassage therethrough and having an inlet and an outlet end and a testingsection between such ends, said duct having two rst opposite plane andparallel walls, the other two second opposite walls being initiallyconvergent at the inlet end and then at least generally parallel, two,similar confronting oppositely disposed rigid bosses located in theduct adjacent the inlet end thereof, said bosses each having a planeouter face engaging a first inner wall of the duct and a streamlinedconvex inner face forming a portion of the wall of the passage, andmeans for simultaneously and similarly displacing the bosseslongitudinally of the duct toward and away from the inlet end thereoffrom a furthest outwardly adjusted position in which at least theforward ends of the bosses lie within the inlet end of the duct to afurthest inwardly adjusted position in which the bosses lie retractedinto the duct beyond the convergent portions of the second walls of thewind tunnel, so as to vary the crossesectional area of the inlet end ofthe Wind tunnel.

5. A wind tunnel as claimed in claim 4, in which they bosses arenarrower than the width of the rst walls and lie substantially centrallyof their respective first walls.

6. A wind tunnel as claimed in claim 5, in which the bosses aresymmetrical about their common longitudinal mid-plane normal to the irstWalls of the tunnel, and the inner face of each boss is smoothly convex.

References Cited in the file of this patent UNITED STATES PATENTS2,229,819 Reid Ian. 28, 1941 2,582,814 Beman et al. Jan. 15, 17952 vFOREIGN PATENTS 969,291 France Dec. 18, 1950

